---
name: "Tk::Error"
section: "3pm"
platform: "linux"
package: "perl-tk"
version: "804.036-9"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Tk::Error"
---

# Tk::Error(3pm)

Method invoked to process background errors

## NAME

Tk::Error - Method invoked to process background errors

## SYNOPSIS

Customization:

```
    require Tk::ErrorDialog;
```

or

```
    sub Tk::Error
    {
      my ($widget,$error,@locations) = @_;
      ...
    }
```

## DESCRIPTION

The **Tk::Error** method is invoked by perl/Tk when a background error occurs. Two possible implementations are provided in the distribution and individual applications or users can (re)define a **Tk::Error** method (e.g. as a perl sub) if they wish to handle background errors in some other manner.

A background error is one that occurs in a command that didn't originate with the application.  For example, if an error occurs while executing a callback specified with a bind or a after command, then it is a background error.  For a non-background error, the error can simply be returned up through nested subroutines until it reaches the top-level code in the application; then the application can report the error in whatever way it wishes.  When a background error occurs, the unwinding ends in the Tk library and there is no obvious way for Tk to report the error.

When Tk detects a background error, it saves information about the error and invokes the **Tk::Error** method later when Tk is idle.

**Tk::Error** is invoked by perl/Tk as if by the perl code:

    *$mainwindow*-\>**Tk::Error**(*"error message"*, *location ...*);

*$mainwindow* is the **MainWindow** associated with widget which detected the error, *"error message"* is a string describing the error that has been detected, *location* is a list of one or more "locations" which describe the call sequence at the point the error was detected.

The locations are a typically a mixture of perl location reports giving script name and line number, and simple strings describing locations in core Tk or perl/Tk C code.

Tk will ignore any result returned by the **Tk::Error** method. If another error occurs within the **Tk::Error** method (for example if it calls **die**) then Tk reports this error itself by writing a message to stderr (this is to avoid infinite loops due to any bugs in **Tk::Error**).

If several background errors accumulate before **Tk::Error** is invoked to process them, **Tk::Error** will be invoked once for each error, in the order they occurred. However, if **Tk::Error** calls **Tk-\>break**, then any remaining errors are skipped without calling **Tk::Error**.

The **Tk** module includes a default **Tk::Error** subroutine that simply reports the error on stderr.

## Tk::ErrorDialog

An alternate definition is provided via:

    `"require Tk::ErrorDialog;"`

that posts a dialog box containing the error message and offers the user a chance to see a stack trace showing where the error occurred.

This is an OO implementation of the Tcl/Tk command **bgerror**, with a twist: since there is only one **ErrorDialog** widget, you aren't required to invoke the constructor to create it; it will be created automatically when the first background error occurs.  However, in order to configure the *-cleanupcode* and *-appendtraceback* **ErrorDialog** options you must call the constructor and create it manually.

The **ErrorDialog** object essentially consists of two subwidgets: a **Dialog** widget to display the background error and a **Text** widget for the traceback information.  If required, you can invoke various widget methods to customize these subwidgets - their advertised names are described below.

    *$mw*-\>**ErrorDialog**(-cleanupcode =\> *code*, -appendtraceback =\> *bool*);

`$mw` is a window reference.

*code* is a CODE reference if special post-background error processing is required (default is undefined). The callback subroutine is called with `@_` having the same arguments that **Tk::Error** was invoked with.

*bool* is a boolean indicating whether or not to append successive tracebacks (default is 1, do append).

### Advertised ErrorDialog widgets

*error\_dialog* is the Dialog widget reference.

*text* is the Text widget reference containing the traceback information.

## BUGS

If **after** or **fileevent** are not invoked as methods of a widget then perl/Tk is unable to provide a *$mainwindow* argument. To support such code from earlier versions of perl/Tk perl/Tk therefore calls **Tk::Error** with string 'Tk' instead: **Tk-\>Tk::Error\\(...\\)**. In this case the **Tk::Error** in **Tk::ErrorDialog** and similar implementations cannot "popup" a window as they don't know which display to use.  A mechanism to supply *the* **MainWindow** in applications which only have one (a very common case) should be provided.

## SEE ALSO

Tk::bind Tk::after Tk::fileevent

## KEYWORDS

background error, reporting